Ok I weigh in at 175. My opponent for 175 backed out, so the event organizer called me up and said that she has 2 opponents lined up for me. One is at 180 and the other at 170. I had to pick one. I picked the one at 170. Did I make the right choice?

5 pounds isn't the end of the world. You don't know your opponents. If all you know is that one is 5 pounds either way then you know little. The 170 could be packing heat why the 180 guy is out of shape.

In the amateurs just train and fight, train and fight, and see where it ends up.